The present invention is directed to air conditioning systems which can allow the introduction of a high percentage fresh air into a building in order to comply with indoor air quality standards in an energy efficient manner.
Basically, the present invention focuses on an outdoor air treatment and ventilation system to deliver properly conditioned outdoor air in HVAC systems. The primary benefit in using this type of system is the ability to independently heat, cool and/or dehumidify the outdoor ventilating air.
Poor indoor air quality can pose many risks for the building designer, owner and manager. The quality of the indoor environment can affect the health and productivity of the building occupants and even affect the integrity of the building structure itself. A building""s indoor air quality is the result of the activities of a wide variety of individuals over the lifetime of a building, the atmosphere surrounding the building, the building materials themselves, and the way in which the building is maintained and operated. The interaction of these variables make achieving acceptable indoor air quality a complex, multi-faceted problem. Although complex, the fundamental factors which directly influence indoor air quality can be divided into four categories: (a) contaminant source control, (b) indoor relative humidity control, (c) proper ventilation, and (d) adequate filtration.
Ventilation is the process of introducing conditioned outside air into a building for the purpose of diluting contaminants generated within the spaces and of providing makeup air to replace air which is lost to building exhaust. The amount of ventilation air so required is established by building codes and industry standards, and varies with the intended use of the occupied spaces. Most building codes reference ASHRAE Standard 62-89 xe2x80x9cVentilation for Acceptable Indoor Air Qualityxe2x80x9d either in part or in entirety as a minimum requirement for ventilation system design. This standard is hereby incorporated by reference. ASHRAE Standard 62-89 recommends that xe2x80x9crelative humidity in habitable spaces be maintained between 30 and 60 percent to minimize the growth of allergenic and pathogenic organismsxe2x80x9d. Additionally, indoor relative humidity levels above 60 percent promote the growth of mold and mildew, can trigger allergenic reactions in some people, and have an obvious effect on personal comfort. Extended periods of high humidity can damage furnishings and even damage the building structure itself. Controlling moisture levels within the building and the HVAC system is the most practical way to manage microbial growth.
The increased attention to indoor air quality (IAQ) is causing system designers to look more carefully at the ventilation and humidity control aspects of mechanical system designs particularly including dedicated outdoor air treatment and ventilation systems. These types of systems separate the outdoor air conditioning duties from the recirculated air conditioning duties. The present invention is intended to encompass all air conditioning systems including air handler systems, variable air volume (VAV) systems and constant volume systems.
A problem occurs during the operation of a high percentage fresh air refrigeration unit having a series connected condenser and reheat coil. As cold air from the evaporator is directed over the reheat coil, refrigerant temperature drops and the refrigerant condenses. Hot gas from the compressor flowing through the reheat coil will first give up its superheat. If the refrigerant in the reheat coil is able to be cooled further, the refrigerant will begin to condense. This condensed liquid then flows to the outdoor condenser which has air flowing through the outdoor condenser coil at a higher temperature than the air flowing through the reheat coil. Consequently, the condensed refrigerant may actually re-evaporate, or at least fail to subcool. The result is insufficient subcooling at the expansion valve.
It is an object, feature and advantage of the present invention to solve the problems of prior art systems.
It is an object, feature and advantage of the present invention to provide an arrangement to reheat cold saturated air to a more comfortable drybulb temperature before being introduced into an inhabited space and to avoid overcooling the space. It is a further object, feature and advantage of the present invention to modulate this reheat using xe2x80x9cfreexe2x80x9d energy from the condensed refrigerant gas in a partially flooded reheat condenser coil.
It is an object, feature and advantage of the present invention to use liquid refrigerant for flooding of a reheat coil piped in parallel with an outdoor condenser coil to control the amount of heat which is rejected to the supply air stream. It is a further object, feature and advantage of the present invention to eliminate separate subcooling sections in the condenser coil and replace those subcooling section with a single subcooler located in the supply air stream. It is a still further object, feature and advantage of the present invention to position the subcooler in the general location of the reheat coil. It is a yet further object, feature and advantage of the present invention to locate the receiver just upstream of the subcooler.
It is an object, feature and advantage of the present invention to provide a reheat coil and an outdoor condenser coil arranged in a parallel refrigerant circuiting arrangement. It is a further object, feature and advantage of the present invention to control the refrigeration system with a modulating liquid valve downstream of the reheat coil. It is an object, feature and advantage of the present invention to provide a retrofit parallel piped hot gas reheat coil. It is a further object, feature and advantage of the present invention to provide subcooling of partially condensed hot gas leaving the hot gas reheat coil and to manage the refrigerant charge required in dehumidification and cooling operating modes. It is a further object, feature and advantage of the present invention to accomplish this using the existing subcooling circuit in the existing condenser coil and by sizing the return piping from the reheat coil in order to match the required charge in the dehumidification mode.
The present invention provides a refrigeration system. The system comprises a supply air duct; an indoor heat exchange coil operably positioned in the supply air duct; a reheat heat exchange coil operably positioned in the supply air duct; an outdoor heat exchange coil; at least one compressor; and an expansion device. The system also comprises refrigeration system tubing connected to and serially arranging the compressor, the outdoor heat exchange coil, the expansion device and the indoor coil into a refrigeration circuit; and reheat tubing connecting the reheat coil to the refrigeration tubing so as to arrange the reheat coil in a parallel circuited arrangement with the outdoor heat exchange coil and in a series circuited arrangement with the compressor, the expansion device and the indoor heat exchange coil. The system also comprises a subcooler located between and operably connected to the indoor heat exchange coil and the parallel circuited arrangement.
The present invention also provides a method of arranging a refrigeration system including an indoor heat exchanger, a reheat coil, an expansion device, an outdoor heat exchanger, and a compressor. The method comprises the steps of: placing the indoor heat exchanger in a supply air stream; placing the reheat coil in the supply air stream; sequentially linking the compressor, the outdoor heat exchanger, the expansion device and the indoor heat exchanger with tubing into a first refrigeration circuit; and linking the reheat coil, with additional tubing, to the first refrigeration circuit so as to place the reheat coil in a series arrangement with the compressor, expansion device, and indoor heat exchanger and in a parallel arrangement with the outdoor heat exchanger.
The present invention further provides a method of controlling reheat in a refrigeration system. The system includes an outdoor coil in parallel arrangement with a reheat coil and includes a flow control valve downstream of the reheat coil. The method comprises the steps of: closing the valve to block flow from the reheat coil thereby causing refrigerant to condense within the reheat coil until the reheat coil is completely filled with liquid; opening the liquid valve slightly to allow refrigerant to flow out of the reheat coil and cause condensation to begin to occur in the reheat coil; and opening the valve completely to expose more coil surface of the reheat coil and cause the reheat coil to be more active in a condensation process.
The present invention additionally provides a refrigeration system. The system comprises a reheat coil; a liquid control valve; and an outdoor coil. The system also comprises first refrigerant tubing operably connected to the outdoor coil, the reheat and the liquid control valve to place the reheat coil and valve in a series arrangement with the valve downstream of the reheat coil and to place the outdoor coil in a parallel arrangement with the reheat coil and the valve.
The present invention still further provides a refrigeration system. The system comprises a supply air duct; an indoor heat exchange coil operably positioned in the supply air duct; a reheat heat exchange coil operably positioned in the supply air duct; an outdoor heat exchange coil; at least one compressor; and an expansion device. The system also comprises refrigeration system tubing connected to and serially arranging the compressor, the outdoor heat exchange coil, the expansion device and the indoor coil into a refrigeration circuit; and reheat tubing connecting the reheat coil to the refrigeration tubing so as to arrange the reheat coil in a parallel circuited arrangement with the outdoor heat exchange coil and in a series circuited arrangement with the compressor, the expansion device and the indoor heat exchange coil. The system further includes a valve in the reheat tubing operable to control refrigerant flow through the reheat coil. A subcooler downstream of the parallel circuited arrangement may also be included.
The present invention yet further provides a method of arranging a refrigeration system including an indoor heat exchanger, a reheat coil, an expansion device, an outdoor heat exchanger, and a compressor. The method comprises the steps of: placing the indoor heat exchanger in a supply air stream; placing the reheat coil in the supply air stream; sequentially linking the compressor, the outdoor heat exchanger, the expansion device and the indoor heat exchanger with tubing into a first refrigeration circuit; linking the reheat coil, with additional tubing, to the first refrigeration circuit so as to place the reheat coil in a series arrangement with the compressor, expansion device, and indoor heat exchanger, and in a parallel arrangement with the outdoor heat exchanger; and using a control valve in the additional tubing to control refrigerant flow from the reheat coil.